Feedbacks between Arctic climate change and glacial ice discharge: Using seismic observations to constrain water transport to the bed of the Greenland Ice Sheet

Some
of the most dramatic predicted effects of climate change, including global sea
level rise and the alteration of ocean circulation patterns, result from the
response of polar ice sheets to rising global temperature. Until recently it was believed that the response
of thick (> 1 km) ice sheets to climate change would be relatively slow due
to the long time scales (~1000 yr) needed for temperature variations at the
surface to reach the bed via thermal conduction and diffusion. Recent observations from the Greenland Ice
Sheet, however, suggest that ice sheets have the potential to respond much more
rapidly and dramatically to climate change than was previously believed. Specifically, new data show ice-flow
acceleration on time scales of days to weeks following the onset of surficial
melting, suggesting that meltwater drains advectively through the ice sheet,
rapidly lubricating and warming the bed. Understanding the mechanisms of meltwater transport is thus critical for
incorporating these feedbacks into models of ice-sheet evolution and for
estimating the rates and magnitudes of past and future ice sheet drawdown and
sea level change.

One mechanism that has
been proposed to rapidly transport meltwater from the surface to the bed of an
ice sheet is the propagation of water-filled fractures that initiated beneath
supraglacial lakes that form annually at the surface. However, while theoretical models suggest
this is a plausible transport mechanism, water-filled crack propagation has
never been observed in thick subfreezing ice sheets. As part of the WHOI Arctic Initiative we
propose to deploy a new network of seismometers around two supraglacial lakes
on the Greenland Ice Sheet. These lakes
are currently being monitored by as part of a 3-year NSF project and have been
observed to drain seasonally. The
proposed seismic network will enable us to constrain seismicity (i.e.,
icequakes) associated with lake drainage and determine 1) whether crack
propagation coincides with drainage and 2) the maximum depth extent of crack
penetration. These measurements would
provide the first direct evidence for rapid meltwater transport from
supraglacial lakes to the bed of Greenland Ice Sheet.

Last updated: September 14, 2010

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